The overall objectives of the proposed research are to determine the pathogenetic mechanisms by which group A streptococci cause infections and their sequels, rheumatic fever and acute glomerulonephritis, so that these diseases may be better prevented or controlled. Three major lines of investigation will be followed: 1) Studies of the immunology of M proteins and lipoteichoic acids which relate to the issues of the development of streptococcal vaccines, the toxicity of these products to man, and their role in infection by group A streptococci. 2) The nature of the streptococcal infections and the properties of the streptococcal strains which produce either rheumatic fever, acute glomerulonephritis or neither sequel. 3) The identification of antigens in the urine of patients with glomerulonephritis which react with streptococcal antisera from rabbits injected with live streptococci.